1. Field of the Invention
This invention relates to an injection molding apparatus and method for molding articles from a thermoplastic material. More particularly, this invention relates to an injection molding apparatus and method by which articles are sequentially formed in a mold assembly that is made up of separable mold halves, which repeatedly close and open relative to one another during each molding cycle.
2. Description of the Prior Art
Many types of useful articles, for example, preforms or parisons of hollow containers, are produced by injection molding from a suitable thermoplastic material, such as high density polyethylene, polypropylene or polyethylene terephthalalate. Injection molding apparatus for molding such articles includes a plurality of mold assemblies, each mold assembly containing a core pin, around which the article is molded, and a separable pair of mold halves that open and close with respect to one another around the core pin to define, when closed, a mold cavity that corresponds in size and shape to the desired outline of the article being molded. A suitable thermoplastic resin at an elevated temperature suitable for molding is introduced into the mold assembly through a gate at an end thereof, from an injection nozzle and co-axially of the mold assembly, to fill the portion of the mold cavity that surrounds the exterior of the core pin, to thereby form the article being molded. U.S. Pat. No. 5,340,304 (Nakamura) discloses injection molding apparatus that generally corresponds to the foregoing description of known, plastic article injection molding devices.
In known plastic article injection molding devices, the mold halves that define the mold cavity are usually symmetrical, (at least when the article being molded is substantially symmetrical) and a nozzle is provided to introduce the moldable plastic resin into the mold cavity through a gate therein. The resin must be introduced substantially along the parallel axes of the mold cavity and the core pin for proper circumferential distribution of the resin within the mold cavity. When the mold halves are symmetrical as taught by the prior art, the nozzle will make contact with both mold halves, and opening and closing of the mold assembly while the nozzle is in contact therewith can lead to impact damage to the nozzle, often requiring replacement of the nozzle after limited use thereof.
Injection molding apparatus according to the present invention includes partable mold halves surrounding a core pin to define a mold cavity for molding a hollow article from a thermoplastic material. However, the mold halves are non-symmetrical with respect to one another, and a first one of the mold halves has an extension at its thermoplastic material receiving end to permit a nozzle for introducing thermoplastic material into the mold cavity to seat solely and entirely in the first mold half. Thus, the mold halves can be separated from one another solely by moving the second mold half away from the first mold half, and no nozzle contact need occur between the nozzle and either of the mold halves during the opening and closing of the mold halves, which helps to prevent impact damage to the nozzle as a result of the opening and closing of the mold assembly.
Accordingly, it is an object of the present invention to provide an improved injection molding apparatus and method for molding articles from a moldable thermoplastic material. More particularly, it is an object of the present invention to provide an injection molding apparatus and method of the foregoing character that avoids the possibility of contact damage of the thermoplastic material injection nozzle as the separable mold halves open and close with respect to one another.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and to the following brief description thereof, to the detailed description of the preferred embodiment and to the appended claims.